Cancer is the second leading cause of death worldwide. It is generally agreed that early diagnosis of the disease is almost always a prerequisite of successful treatment. For decades, cancer diagnostic methods have been based on morphological examination of surgically removed tissues. However, this approach has significant limitations for predicting the progression of the cancer cells such as inaccuracy and requirement for large amounts of biological materials. Furthermore, morphological examination of these cancer cells requires highly trained personnel to be able to distinguish cancer cells from normal cells. Due to these limitations, a number of scientists have developed other types of cancer diagnostic methods, for example a biomarker that uses biological, chemical or biophysical indicator of an underlying biological process to indicate or determine a particular disease state. Another method is by detecting the cell growth using a MEMS (microelectromechanical system) biosensor device that merges biological knowledge and microelectronics technology.
Recently, MEMS technology expands in an extremely fast pace. It is used in various applications such as actuators, accelerometer, pressure sensors, chemosensors, gyroscopes, optical switching technology and more. Nevertheless, MEMS technology is also used in biological fields for the construction of biosensors. Generally, a MEMS biosensor is an analytical device with the combination of biotechnology and microelectromechanical system that converts a biological response to electrical signal. A MEMS biosensor can be used as a device to measure chemicals and micro-organisms in wide range of environments and as a biological system to detect complex materials. Nowadays, MEMS biosensors have become widespread use in a wide variety of applications such as diagnostics, therapeutics and tissue engineering. There are a few types of biosensor used in the industry such as calorimetric, potentiometric, amperometric, surface acoustic wave and more. In calorimetric biosensors, the change in temperature of a solution containing analyte is measured whereby in potentiometric biosensors, electrical potential is produced due to the changed distribution of electrons. As for amperometric biosensors, the analyte undergoes a redox reaction and the current in an electrochemical cell. A surface acoustic wave biosensor is a biosensor based on the measurement of resonant frequency of the surface acoustic wave. Various types of biosensors have been developed including the combinations of different types of biosensors, for example, an amperometric-potentiometric biosensor that includes both amperometric method and potentiometric method in detecting cell growth.
Several prior arts have disclosed applications related to construction of MEMS biosensors for detecting cell growth. One of the prior art is U.S. Pat. No. 5,135,852 which discloses a piezoelectric biosensor for detecting metabolic growth requirement, antibiotic responses and specific bacterial products of microorganisms. Generally, the more sensing methods integrated into a biosensor device enhances the performance of the biosensor device. However, this prior art utilizes only one type of sensing method in the biosensor which is a piezoelectric biosensor to observe the change in resonant frequency in order to detect the mass change of the living organism. Therefore due to the patent limited applicability, it is said to be not feasible in constructing a MEMS biosensor for detecting cell growth.
U.S. Pat. No. 5,981,268 has disclosed an apparatus and method for monitoring changes in cells upon addition of an analyte to the environment of the cell. In this prior art, only one detecting method is used, which is by monitoring the impedance changes of the cell, to detect the changes in the cell. This prior art has its drawbacks due to the limited sensing methods as more sensing methods can be integrated into one biosensor to monitor the change of a cell more accurately. Therefore due to the patent limited applicability, it is said to be not feasible in constructing a MEMS biosensor for detecting cell growth.